Recently, in radio communication, and mobile communication in particular, various kinds of information such as image and data in addition to speech are targeted for transmission. Demands for higher speed transmission are expected to further increase in the future, and radio transmission techniques that efficiently use limited frequency resources and realize high transmission efficiency are in demand to perform high speed transmission.
One radio transmission technique that responds to these demands is OFDM (Orthogonal Frequency Division Multiplexing). OFDM is a multicarrier transmission technique of transmitting data in parallel using many subcarriers, has features such as high-frequency efficiency and reduced inter-symbol interference in a multipath environment, and is known to be effective in improving transmission efficiency.
Studies are underway to perform frequency scheduling when this OFDM is used in a downlink and data for a plurality of radio communication mobile station apparatuses (hereinafter simply “mobile stations”) is assigned to a plurality of subcarriers (e.g., see Non-Patent Document 1). According to frequency scheduling, a radio communication base station apparatus (hereinafter simply “base station”) adaptively assigns subcarriers to mobile stations based on received qualities of frequency bands of the mobile stations, so that it is possible to obtain a maximum multi-user diversity effect and perform communication quite efficiently.
Frequency scheduling is generally performed in units of resource blocks (RB's) acquired by making sets of several subcarriers into blocks. Furthermore, there are two assignment methods in frequency scheduling, namely, localized assignment, which is assignment in units of a plurality of consecutive subcarriers, and distributed assignment, in which assignment is performed for a plurality of distributed inconsecutive subcarriers.
Furthermore, the assignment result of frequency scheduling performed in a base station is reported to mobile stations using a shared control channel (SCCH). Further, studies are underway to report an assignment result of the frequency bandwidth of 5 MHz with one SCCH (e.g., see Non-Patent Document 2).    Non-Patent Document 1: R1-050604 “Downlink Channelization and Multiplexing for EUTRA”, 3GPP TSG-RAN WG1 Ad Hoc on LTE, Sophia Antipolis, France, 20-21 Jun., 2005    Non-Patent Document 2: R1-060032, “L1/L2 Control Channel Structure for E-UTRA Downlink”, NTT DoCoMo, 3GPP TSG-RAN WG1 LTE Ad Hoc Meeting contribution, 2006/01